1. Field of the Invention
The present invention relates to a transistor and a manufacturing method thereof, and more particularly, to an oxide semiconductor transistor including a ferroelectric material layer and a method of forming the same.
2. Description of the Prior Art
Oxide semiconductor materials, such as indium gallium zinc oxide (IGZO), have been applied in thin film transistors (TFTs) of display devices and field effect transistors (FETs) used in integrated circuits because of properties such as high mobility and low leakage current. However, although the leakage current of the transistor including the oxide semiconductor layer is relatively low, the application field of the present oxide semiconductor transistor is still limited because the threshold voltage (Vt) of the oxide semiconductor transistor is still too high and the on-current (Ion) of the oxide semiconductor transistor is not high enough for some application such as low power devices. For example, the gate insulation layer in the oxide semiconductor transistor has to be thick enough (thicker than 100 angstroms for example) for keeping low leakage current, and the on-current is limited by the thicker gate insulation layer. The gate voltage (Vg) and the drain voltage (Vd) are also too high because of the relatively higher threshold voltage of the oxide semiconductor transistor, and the oxide semiconductor transistor cannot be applied in the low power devices accordingly. Therefore, it is an important subject for the related industries to improve the electrical performances of the oxide semiconductor transistor without deteriorating the original property of low leakage current.